As is known in the art, hydrogen chloride readily absorbs in water. One well known technique for the production of aqueous hydrochloric acid is the use of a so-called adiabatic absorber unit. In using this technique, feed gas containing hydrogen chloride is fed to the bottom of a contact tower. The gas is counter-currently contacted by the absorbing medium (typically water). As is recognized in the art, the term "adiabatic" is a misnomer since the process is operated as an isothermal process (constant temperature) rather than an adiabatic process (constant enthalpy). Acid strengths up to 34% are easily made in the known adiabatic systems. However, attempts to produce stronger acid results in a rapid decrease in absorption efficiency. Background information relative to the known adiabatic process can be found in Chemical Engineering Progress, Vol. 69, No. 2, February, 1973, pages 50-52, "Adiabatic and Falling Film Absorption of Hydrogen Chloride", C. E. Hulswitt; and, U.S. Pat. No. 3,807,139. Finally, a relatively complex process is known for the production of 35.5% hydrogen chloride, which process requires at least two separate absorption units. See U.S. Pat. No. 3,666,424.
It is an object of the present invention to continuously produce aqueous hydrochloric acid having a concentration of at least 35.5% by weight, and preferably from 35.5 to 37% by weight, in a simple and efficient process.